There are an increasing number of telecommunication services being proposed which, if fully implemented, could use up the allocated frequency spectrum. It is important to be able to provide such services without one service interfering with the other. If a service occupies the same frequency at the same time, there is a possibility of interference between the services which results in spectrum conflicts.
As will be described, so-called cognitive radios, which may employ software defined radio platforms, are capable of tailoring the transmitted output from the radio. With the advent of software defined radios, it is possible to alter the modulation type, frequency and the time of transmission to guarantee the transmission will not interfere with existing signals. Such radios may be adjusted, for instance, to inhibit transmission during times in which other signals exist. The signals from the software defined radios can also be controlled to emit non-interfering modulation formats. Programs such as the Next Generation (XG) communications funded by the Defense Advance Research Projects Agency (DARPA) propose systems where from radio scene analysis, one finds spectrum holes or White space which defines where signals may be transmitted without interference with other signals. Thus, White space refers to spaces that are not occupied by a signal.
While such systems create conditions for transmission such that the transmitted signal does not interfere with other existing signals, spectrum utilization with such techniques is somewhat limited.
As will be discussed, and as part of the subject invention, it has been found that there are so-called Gray spaces where signals only partially occupy the signal space. If it were possible to be able to detect not only White spaces but also Gray spaces, then the spectrum could be more fully utilized, assuming that one could transmit non-interfering signals in the White and Gray spaces.
Moreover, by analyzing the signal space for existing signals and providing predictors as to the future behavior of these signals, one can accurately predict future White space and Gray space. This permits robust tailoring of the transmitted signals so as not to interfere either with future signals.
More specifically, as telecommunications equipment evolves in capability and complexity, and Multiple-Input and Multiple-Output (MIMO) and Multi-User Detection (MUD) systems push the system throughput to its limits, it is not going to be too long before cognitive radios will reach the market place (J. Mitola, Cognitive Radio: An Integrated Agent Architecture for Software Defined Radio, Ph. D. Thesis, Royal Institute of Technology, Sweden, Spring 2000; and S. Haykin, “Cognitive Radio: Brain-Empowered Wireless Communications,” IEEE J. Select. Areas Commun., vol. 23, no. 2, pp. 201-220, February 2005).
In fact the IEEE 802.22 Working Group (IEEE Working Group 802.22, http://grouper.ieee.org/groups/802/22/, on Wireless Regional Area Networks (“WRANs”)), has been looking to develop a standard for a cognitive radio-based PHY/MAC/air interface for use by license-exempt devices on a non-interfering basis in spectrum that is allocated to the TV Broadcast Service on Wireless Regional Area Networks (WRAN). Ad hoc groups under the Project Authorization Request (PAR) approved by the IEEE-SA Standards Board have started developing a cognitive radio-based PHY/MAC/air interface for use by license-exempt devices on a non-interfering basis in spectrum that is allocated to the TV Broadcast Service. Moreover, cognitive radios will help the commercial as well as the military communication systems, by doing away with the need for comprehensive frequency planning. It is contemplated cognitive radios will be capable of sensing their environment, making decisions on the types of signals present, learning the patterns and choosing the best possible method of transmitting the information. They will be situation aware, and capable of making decisions to ensure error-free and smooth transfer of bits between the users. Cognitive radios will be based on software defined radio (SDR) platforms and will try to understand not only what the users want but also what the surrounding environment can provide.